[ATL/WTL]_[初级]_[Win32实现Cocoa的dispatch_async到主线程的异步消息处理]

场景

1.写界面程序时, 大多是底层部分需要至少一个工作线程来处理逻辑, 避免使用主线程导致界面卡顿, 当底层线程处理数据完毕后, 需要转发到主线程绘制数据. 因为非绘图线程绘制数据会导致不可预料的问题, 一般情况下会导致程序莫名其妙崩溃，多线程同时调用绘制函数会导致资源冲突，而且冲突可能会在特定情况下才发生，不易察觉.

2.工作线程发送数据到主线程，Win32消息处理一般有几种方式 PostMessage,SendMessage,PostThreadMessage, 或者自己实现的信号量通讯.

3.一般情况下我们通过PostMessage发送消息, 指定自定义消息类型, 之后传数据指针到WPARAM, 类型给LPARAM, 之后在接收的窗口类里进行捕抓和处理, 通过LPARAM来进行 switch 处理, 这样坏处就是
– 处理代码都放到统一的地方, 代码量增大时会造成维护困难.
– 需要写一个枚举集合来存储处理类型, 便于分开处理不同的业务逻辑.
– 需要封装数据对象，由于不同的业务处理涉及不同的数据对象, 可能会需要创建很多不同的数据结构.
– 业务相关的逻辑被强制分离, 导致不便于追踪和调试.

说明

1.macOS 的Cocoa提供了一种Grand Central Dispatch方式来异步出来逻辑, 还支持lambda表达式, 让业务逻辑更有序, 便于程序员逐步跟踪, 可惜Win32没有提供那么方便的技术, 不过不妨碍我们写一个. 像下边这种的需要打开一个窗口选择文件或更新某个进度条，某个按钮最常见.

BASObserveData *bsd = (BASObserveData*)malloc(sizeof(BASObserveData));*bsd = *data;dispatch_async(dispatch_get_main_queue(), ^(void){        NSOpenPanel *panel = [NSOpenPanel openPanel];        [panel setPrompt:@"Confirm"];        [panel setCanChooseDirectories:NO];        [panel setCanCreateDirectories:NO];        [panel setCanChooseFiles:YES];        [panel setAllowsMultipleSelection:YES];        [panel setMessage:@"Please select backup file(s)."];        [panel beginSheetModalForWindow:[NSApp mainWindow] completionHandler:^(NSInteger result) {            if (result == NSFileHandlingPanelOKButton)            {                NSArray* pathUrls= [[panel URLs] retain];                bsd->send_userdata = pathUrls;                bsd->id = kCommCommandBookImportToJson;                bsd->data_int = MyCommProgressTypeDevice;                [UiNotificationCenter SendCommand:LIBCOMM_COMMAND_DO_BOOLK setBASObserveData:bsd];            }            free(bsd);            free((char*)bsd->data_str);        }];    });

2.我们可以模仿 dispatch_async(dispatch_get_main_queue(), ^(void){}); 写一个Win32的实现, 我用的vs2010, 不完善的C++11, 目前还不支持异步lambda表达式, 所以使用函数代替, 如果项目一开始就使用以下的方式, 的确会少很多bug和精简代码. 这里我使用了std::function和std::bind技术来实现。

例子

1.头文件 dispatch_queue.h

#ifndef __DISPATCH_QUEUE_H#define __DISPATCH_QUEUE_H#include <Windows.h>#include <WinUser.h>#include <functional>#include <atlbase.h>#include <atlapp.h>enum{    WMC_DISPATCH_MAIN_QUEUE = WM_USER+1000};typedef struct DispatchQueueObject1{    DWORD threadId;    HWND m_hwnd;}DispatchQueueObject;extern void DispatchQueueInit(HWND hwnd);extern DispatchQueueObject* DispatchGetMainQueue();// vs2010 可能支持 带捕获方式的lambda 表达式里, 捕获的变量在异步执行 lambda 时会无效.template<class DispatchFunction> void DispatchAsync2(DispatchQueueObject* queue,DispatchFunction func){    std::function<void()>* callback = new std::function<void()>(func);    if(queue->threadId){        ::PostThreadMessage(queue->threadId,        WMC_DISPATCH_MAIN_QUEUE,(WPARAM)callback,0);    }else{        ::PostMessage(queue->m_hwnd,        WMC_DISPATCH_MAIN_QUEUE,(WPARAM)callback,0);    }}inline void DispatchAsync(DispatchQueueObject* queue,std::function<void()>* callback){    if(queue->threadId){        ::PostThreadMessage(queue->threadId,        WMC_DISPATCH_MAIN_QUEUE,(WPARAM)callback,0);    }else{        ::PostMessage(queue->m_hwnd,        WMC_DISPATCH_MAIN_QUEUE,(WPARAM)callback,0);    }}#endif

2.dispatch_queue.cpp

#include "stdafx.h"#include "dispatch_queue.h"static HWND gMainFrameHwnd = NULL;void DispatchQueueInit(HWND hwnd){    gMainFrameHwnd = hwnd;}DispatchQueueObject* DispatchGetMainQueue(){    DispatchQueueObject* object = (DispatchQueueObject*)malloc(sizeof(DispatchQueueObject));    memset(object,0,sizeof(DispatchQueueObject));    object->m_hwnd = gMainFrameHwnd;    return object; }

3.在进入循环前调用 DispatchQueueInit(wndMain.m_hWnd);

int Run(LPTSTR /*lpstrCmdLine*/ = NULL, int nCmdShow = SW_SHOWDEFAULT){    CMessageLoop theLoop;    _Module.AddMessageLoop(&theLoop);    CMainFrame wndMain;    if(wndMain.CreateEx() == NULL)    {        ATLTRACE(_T("Main window creation failed!\n"));        return 0;    }    DispatchQueueInit(wndMain.m_hWnd);    wndMain.ShowWindow(nCmdShow);    int nRet = theLoop.Run();    _Module.RemoveMessageLoop();    return nRet;}

4.在主窗口注册接收消息处理函数 MESSAGE_HANDLER(WMC_DISPATCH_MAIN_QUEUE, OnDispatchMainQueueEvent), 使用例子看 OnFileNew. 运行程序点击菜单 File->New

// MainFrm.h : interface of the CMainFrame class///////////////////////////////////////////////////////////////////////////////#pragma once#include "dispatch_queue.h"#include <iostream>#include <string>#include <sstream>#include <assert.h>void PrintStr(std::wstring* str){    assert(_Module.m_dwMainThreadID == ::GetCurrentThreadId());    std::wstringstream wss;    wss << *str << L" m_dwMainThreadID: " << _Module.m_dwMainThreadID << L"\n";    std::wstring str1 = wss.str();    OutputDebugString(str1.c_str());    delete str;}DWORD WINAPI StartThread(void* data){    std::wstringstream wss;    wss << L"work GetCurrentThreadId():" << GetCurrentThreadId() << L"\n";    std::wstring str1 = wss.str();    OutputDebugString(str1.c_str());    auto str = new std::wstring(L"helloworld");    auto callback = new std::function<void()>(std::bind(PrintStr,str));    DispatchAsync(DispatchGetMainQueue(),callback);    return 0;}class CMainFrame :     public CFrameWindowImpl<CMainFrame>,     public CUpdateUI<CMainFrame>,    public CMessageFilter, public CIdleHandler{public:    DECLARE_FRAME_WND_CLASS(NULL, IDR_MAINFRAME)    CDispatch_async_testView m_view;    virtual BOOL PreTranslateMessage(MSG* pMsg)    {        if(CFrameWindowImpl<CMainFrame>::PreTranslateMessage(pMsg))            return TRUE;        return m_view.PreTranslateMessage(pMsg);    }    virtual BOOL OnIdle()    {        return FALSE;    }    BEGIN_UPDATE_UI_MAP(CMainFrame)    END_UPDATE_UI_MAP()    BEGIN_MSG_MAP(CMainFrame)        MESSAGE_HANDLER(WMC_DISPATCH_MAIN_QUEUE, OnDispatchMainQueueEvent)        MESSAGE_HANDLER(WM_CREATE, OnCreate)        MESSAGE_HANDLER(WM_DESTROY, OnDestroy)        COMMAND_ID_HANDLER(ID_APP_EXIT, OnFileExit)        COMMAND_ID_HANDLER(ID_FILE_NEW, OnFileNew)        COMMAND_ID_HANDLER(ID_APP_ABOUT, OnAppAbout)        CHAIN_MSG_MAP(CUpdateUI<CMainFrame>)        CHAIN_MSG_MAP(CFrameWindowImpl<CMainFrame>)    END_MSG_MAP()// Handler prototypes (uncomment arguments if needed)://  LRESULT MessageHandler(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, BOOL& /*bHandled*/)//  LRESULT CommandHandler(WORD /*wNotifyCode*/, WORD /*wID*/, HWND /*hWndCtl*/, BOOL& /*bHandled*/)//  LRESULT NotifyHandler(int /*idCtrl*/, LPNMHDR /*pnmh*/, BOOL& /*bHandled*/)    LRESULT OnDispatchMainQueueEvent(UINT uMsg, WPARAM wParam, LPARAM lParam, BOOL& bHandled)    {        std::function<void()>* func = (std::function<void()>*)wParam;        (*func)();        delete func;        return 0;    }    LRESULT OnCreate(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, BOOL& /*bHandled*/)    {        m_hWndClient = m_view.Create(m_hWnd, rcDefault, NULL, WS_CHILD | WS_VISIBLE | WS_CLIPSIBLINGS | WS_CLIPCHILDREN, WS_EX_CLIENTEDGE);        // register object for message filtering and idle updates        CMessageLoop* pLoop = _Module.GetMessageLoop();        ATLASSERT(pLoop != NULL);        pLoop->AddMessageFilter(this);        pLoop->AddIdleHandler(this);        return 0;    }    LRESULT OnDestroy(UINT /*uMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, BOOL& bHandled)    {        // unregister message filtering and idle updates        CMessageLoop* pLoop = _Module.GetMessageLoop();        ATLASSERT(pLoop != NULL);        pLoop->RemoveMessageFilter(this);        pLoop->RemoveIdleHandler(this);        bHandled = FALSE;        return 1;    }    LRESULT OnFileExit(WORD /*wNotifyCode*/, WORD /*wID*/, HWND /*hWndCtl*/, BOOL& /*bHandled*/)    {        PostMessage(WM_CLOSE);        return 0;    }    LRESULT OnFileNew(WORD /*wNotifyCode*/, WORD /*wID*/, HWND /*hWndCtl*/, BOOL& /*bHandled*/)    {        // TODO: add code to initialize document        DWORD IDThread2;        HANDLE h2 = CreateThread(NULL,0,(LPTHREAD_START_ROUTINE) StartThread,NULL,0,&IDThread2);        return 0;    }    LRESULT OnAppAbout(WORD /*wNotifyCode*/, WORD /*wID*/, HWND /*hWndCtl*/, BOOL& /*bHandled*/)    {        CAboutDlg dlg;        dlg.DoModal();        return 0;    }};

输出

work GetCurrentThreadId():6880helloworld m_dwMainThreadID: 4836

参考

Windows 消息循环初解
dispatch_async

下载

vs2010项目下载